Download ICRP 129 RP in CBCT

ICRP Publication 129
Authors on behalf of ICRP
M.M. Rehani, R. Gupta, S. Bartling, G. C. Sharp, R. Pauwels, T. Berris, J. M. Boone
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 This slide set copies information from ICRP
Publication 129 in Main Points and in
Recommendations
 Readers of this slide set are advised to go through
the full publication for detailed information as this
material is only a glimpse, rather than being a
comprehensive presentation of contents
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Introduction
CBCT Technology
The Biological Effects of Radiation
Principles of Radiological Protection for Patients and
Workers
Assessing Patient Doses in CBCT
Optimisation of Protection of Patients and Workers in
CBCT
Radiation Dose Management in Specific Applications of
CBCT
Training Considerations for CBCT
Quality Assurance Programmes
Recommendations
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 CBCT extends the use of CT to areas that were not
typically associated with CT imaging in the past, e.g.
surgery, dental and otolaryngology (ear-nose-throat,
ENT) imaging, angiography suites, radiotherapy
treatment vaults, and orthopaedic imaging.
 The associated radiological protection issues are
substantially different from those of conventional CT.
 The perception that CBCT involves lower doses was
only true in initial applications. CBCT is now used
widely by specialists who have little or no training in
radiological protection.
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ICRP P129 p.13 and p 9
 The manufacturers of CBCT scanners have
invested considerable effort into meeting the
electrical and mechanical safety requirements of
the users. Similar diligence is needed for issues
related to radiation dose and radiological
protection.
 This document provides a basis to develop
informed decisions and to direct the usage of
CBCT for optimising the trade-off between
clinical benefit and radiation risk.
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 The ICRP emphasises that protection should be
optimised not only for whole-body exposures, but
also for exposures to specific tissues, especially
those of the lens of the eye, thyroid, breast, heart,
and cerebrovascular system.
 Equipment used for both fluoroscopy and CBCT
should provide aggregate dose indices for individual
patients during the entire procedure through
electronic display on the operator console and a
radiation dose structured report (RDSR file).
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 Optimisation of both patient and worker doses,
particularly when the worker has to be near the modality,
is important wherein monitoring of doses become an
essential tool. Recording, reporting and tracking of
radiation dose for an individual patient should be made
possible in a consistent manner across vendors.
 Low dose protocols may be sufficient for diagnostic
procedures focused on high-contrast structures, such as
lung, bones, dental and maxillofacial scans, ENT scans
(paranasal sinuses, skull, temporal bone), interventional
material, and contrast-enhanced vessels (angiographic
interventions).
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 Protocols with higher dose should only be
selected if visualisation of low-contrast
structures such as intracranial haemorrhage,
soft-tissue tumours, or abscesses are the
primary focus.
 Most interventional and intra-procedural C-arm
CBCT systems can scan an angular range
spanning 180o to 240o + the cone angle of the xray beam. Localised critical organs, such as the
thyroid, eyes, female breasts and gonads, should
be on the “detector side” of the arc, whenever
possible.
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 Clinical need permitting, every effort should be made
by users to ensure the volume of interest is fully
incorporated in the field of view (FOV) provided by
the CBCT scanners while radiosensitive organs are
placed outside the FOV.
 The aim of CBCT should be to answer a specific
diagnostic or intra-operative question vis-à-vis other
imaging modalities and not to obtain image quality
that rivals MDCT. The decision by the referring
practitioner to utilise CBCT should be made in
consultation with the imaging professional.
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 There is a need to provide checks and balances,
for example, dose check alerts implemented in
CT in recent years, to avoid unintended high
patient exposure as compared to locally defined
reference values.
 Methods which provide reliable estimates of
patient eye dose under practical situations
should be established and utilised.
 The user of CBCT in interventions can influence
the radiation dose imparted to the patient
significantly by judiciously using a “low-imagequality or low dose” vs. a “high-image-quality or
high dose” scan protocol.
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 In radiotherapy, justified use of CBCT has
potential uses at different stages of therapy such
as: pre-treatment verification of patient position
and target volume localisation, evaluation of
non-rigid misalignments, such as flexion of the
spine or anatomic changes in soft tissue, and
during or after treatment to verify that the patient
position has remained stable throughout the
procedure. Low-dose CBCT protocols should be
used for pre-treatment alignment of bony
structures.
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 Many machines were initially only capable of
fluoroscopy, but can now additionally perform CBCT.
Because of the improved clinical information in
CBCT and its ability to remove overlying structures,
the user may be tempted to over-utilise the CBCT
mode. Users should judiciously use CBCT mode.
 In orthopaedics, justified use of CBCT can help in
assessing the 2 dimensional position of fractures
and implants with respect to the bony anatomy,
especially in situations where fluoroscopy alone is
insufficient, and thus can help in patient dose
management.
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 In urology, low-dose CBCT protocols should be
used when imaging high-contrast structures,
such as calcified kidney stones or device
placements.
 Dental and maxillofacial CBCT scans should be
justified, considering alternative imaging
modalities. Once justified, it should be optimised
to obtain images with minimal radiation dose
without compromising the diagnostic
information.
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 The level of training in radiological protection
should be commensurate with the level of
expected radiation exposure (ICRP, 2009).
 All personnel intending to use CBCT for
diagnostic purposes should be trained in the
same manner as for diagnostic CT and those
intending to perform interventional CBCT should
be in trained in same manner as for
interventional CT.
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1. Expanded availability and newer applications have
put CBCT technology in the hands of medical
professionals who do not traditionally use CT.
ICRP’s radiological protection principles and
recommendations provided in earlier publications,
particularly Publications 87 and 102 apply to these
newer applications and should be adhered to.
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2. As many applications of CBCT involve patient
doses similar to MDCT, the room layout and
shielding requirements in such cases need to be
similar to protect workers adequately.
3. Medical practitioners bear the responsibility for
making sure that each CBCT examination is
justified and appropriate.
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4. When referring a patient for a diagnostic CBCT
examination, the referring practitioner should be aware
of the strengths and weaknesses for CBCT vis-à-vis
MDCT, magnetic resonance imaging, and other
competing imaging modalities. The decision to utilise
CBCT should be made in consultation with an imaging
professional.
5. Manufacturers are challenged to practice standardised
methods for dosimetry and dose display in CBCT in
conformance with international recommendations such
as ICRU. Unfortunately, at present, there is wide
variation in dose quantities and units being displayed in
CBCT machines. The users are often unable to
compare doses among different scanners or protocols.
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6. Use of CBCT systems for both fluoroscopy and
tomography pose new challenges in quantitating
radiation dose. There is a need to develop
methods that aggregate exposures to individual
patients during the entire procedure that may utilise
a combination of fluoroscopy and CBCT during a
given examination.
7. Recording, reporting and tracking of radiation dose
for an individual patient should be made possible in
a consistent manner across vendors.
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8. There is a need to provide checks and balances
(e.g. dose check alerts implemented in CT in
recent years), to avoid unintended high patient
exposure as compared with locally defined
reference values.
9. Positioning radiosensitive organs such as the
thyroid, the lens of the eye, breasts and gonads on
the detector side during the partial rotation scan is
a useful feature in CBCT that needs to be utilised
for radiological protection of these organs.
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10. Many machines were initially only capable of
fluoroscopy, but can now additionally perform
CBCT. Because of the improved clinical information
on CBCT, and its ability to remove overlying
structures, a user may be tempted to over utilise
the CBCT mode. Users must understand that the
CBCT function of their system is not a low-dose
“fluoroscopy run” and use this mode judiciously.
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ICRP, 2015. Radiological Protection in Cone Beam
Computed Tomography (CBCT). ICRP Publication 129.
Ann. ICRP .
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www.icrp.org
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